Maximum Polling for KML Feed

I finally hit a  '429 Too Many Requests' error today from my web app that does some limited live tracking.  I cranked it up to 1 minute polling since the event is using all 2 minute trackers.  When I noticed the error, I turned it off and tried on the hour until requests went through again (took about an hour or two).  I've now got it polling every 10 minutes which seems ok but the fact remains there is no documentation about how much polling is too much!  

I'd love to know how often I can poll per-minute or per-hour and if there is a way to batch KML feed requests together rather than iterating through each feed URL.

Thanks,

Aaron